Description (Applicant Abstract): Phytoplasmas are prokaryotes that cause diseases such as coconut lethal yellowing, aster yellows, elm phloem necrosis, and maize bushy stunt. They are members of the class Mollicutes that have not yet been grown in culture. Therefore, the diseases that they cause are difficult to diagnose or differentiate and knowledge of their genetics is limited. The long-term objective of this research is to better understand the basic biology of phytoplasmas and answer questions about how they interact with their hosts. The aim of this proposal is to use RT-PCR to examine the transcription of fragments of the severe strain of aster yellows (SAY) phytoplasma chromosomal and plasmid DNA. Different mRNAs may be transcribed over the course of infection or in different phytoplasma strains. DNA and amino acid sequences of cloned phytoplasma DNA fragments will be compared to sequences published for other microorganisms to search for similarities. This work will increase understanding of the ways that phytoplasmas interact with their hosts and significantly increase the scientific knowledge in this area. Although these studies will be done with plants and phytopathogens, other members of the class Mollicutes are human and veterinary pathogens and information about host parasite interactions in the phytoplasmas will be applicable to these pathogens as well. Phytoplasma infections of important crop plants can cause a significant impact on human health and well being. Presently pesticides are used to control the insect vectors and antibiotics are used to control the phytoplasmas. However, these may directly and indirectly affect human health. It is possible that a better understanding of phytoplasmas will lead to better methods for their control. The research techniques used are also the same as those used in human or veterinary research.